1. Field of the Invention
The present application relates to systems and methods for performing risk assessment.
2. Background Discussion
The “Probabilistic Risk Assessment Procedures Guide for NASA Managers and Practitioners” defines Probabilistic Risk Assessment (PRA) as follows: “Probabilistic Risk Assessment (PRA) is a comprehensive, structured, and logical analysis method aimed at identifying and assessing risks in complex technological systems for the purpose of cost-effectively improving their safety and performance.” A PRA model often uses a combination of Event Tree (which represents a complex super system of events) and Fault Tree (which represents sub systems of events) models to analyze potential failure scenarios to determine their probability of occurrence, which when combined with an analysis of their effects, provides a quantitative assessment of risk. The combination of ET and FT models has proven effective for the analysis of a variety of critical systems, most notably in the nuclear and aerospace communities. Several software tools support the ET/FT combination for PRA, including QRAS (by Item software) (see, e.g., U.S. Pat. No. 6,223,143, Apr. 24, 2001, Quantitative risk assessment system (QRAS)) and SAPHIRE (by INEL).
With the increasing use of computer-based systems for critical applications, the FT method has expanded to allow for the analysis of failure modes and effects that are unique to these systems. The expansion of the FT methodology to allow the analysis of computer-based systems has resulted in the DFT (Dynamic Fault Tree) methodology. The DFT methodology is seeing increased use in research and industry for a variety of applications. DFT analysis is fully supported by the GALILEO software tool (see, e.g., K. Sullivan, et al., “The Galileo Fault Tree Analysis Tool,” ftcs p. 232; Twenty-Ninth Annual International Symposium on Fault-Tolerant Computing, 1999); in addition, both RELEX and RELIASOFT provide some support for DFT constructs in their reliability analysis software.
In the present application, a new methodology and system (referred to herein as DEFT) allows, among other things, the combination of ET and DFT models for dynamic PRA. DEFT defines the mathematical model that results when the DFT model replaces the FT model within the ET framework. Among other things, the methodology and system effectively extends the PRA methodology to allow its application to complex computer-based systems.
While a variety of systems and methods are known (such as, e.g., shown in the below-listed patents and references), there is a continued need for improved systems and methods.